Radiation coupler

ABSTRACT

Semiconductor photonics devices for coupling radiation to a semiconductor waveguide are described. An example photonics device comprises a semiconductor-on-insulator substrate comprising a semiconductor substrate, a buried oxide layer positioned on top of the semiconductor substrate, and the semiconductor waveguide on top of the buried oxide layer to which radiation is to be coupled. The example device also comprises a grating coupler positioned on top of the buried oxide layer and configured for coupling incident radiation to the semiconductor waveguide. The semiconductor substrate has a recessed portion at the backside of the semiconductor substrate for receiving incident radiation to be coupled to the semiconductor waveguide via the backside of the semiconductor substrate and the grating coupler.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to European Patent Application SerialNo. 13198498.1 filed Dec. 19, 2013, the contents of which are herebyincorporated by reference in their entirety.

FIELD OF THE INVENTION

The present disclosure relates to the field of photonics. Moreparticularly, the present disclosure relates to photonics devices andmethods for coupling radiation from and to an integrated waveguide.

BACKGROUND

Photonics devices are widely prevalent in today's world. One issue inoptical transport for optics communication, processing, or data transferis efficiency when coupling radiation from one medium to another, e.g.from an optical fiber to a photonics device or vice versa. A number ofcoupling arrangements are available at present. One often used couplingelement is a grating element. In order to optimise coupling efficiency,coupling materials and coupling configurations have been suggested.

Some systems make use of the silicon photonics platform. In the siliconphotonics platform, use can be made of SiN as gratings in a SiNwaveguide, having the benefit that SiN has low losses, low thermaldependency and high tolerance to fabrication errors. Furthermore, thesilicon photonics platform offers the advantage that active devices canbe easily incorporated. In order to increase the efficiency of thegrating coupler, one suggestion is to use a mirror layer under a siliconphotonics grating coupler below the buried oxide (BOX) layer of asilicon-on-insulator (SOI) wafer. It was demonstrated that thisincreases the coupling efficiency of the grating from a single modefiber to a single mode silicon waveguide. Such a mirror can, forexample, be a distributed Bragg reflector made of a series ofalternating layers of materials having a large refractive indexdifference (for instance SiO₂ and Si or SiO₂ and SiN) or a reflectivemetal layer such as aluminum. The presence of the reflector increasesthe amount of light reflected at the BOX/Silicon substrate interfacetowards the grating, thus increasing the amount of light coupled. Moreparticularly, only part of the light that hits the grating will coupleto the waveguide while the other part will go through. When a reflectoris present, the part going through the grating will be reflected backtowards the grating having a second chance to couple.

Nevertheless, implementing the reflector below the buried oxide of thesilicon-on-insulator, results in the fact that non-standard, custom madesilicon-on-insulator wafers are to be used, rendering the manufacturingof the photonics device less trivial.

Alternative methods for increasing efficiency are known. In a firstexample, the coupling efficiency of the grating coupler is increased byapplying a silicon grating by locally increasing the silicon waveguidethickness. Nevertheless, the latter requires tight control of thegeometrical dimensions for controlling the grating spectral response. Inanother known example, a mirror is implemented under the grating byperforming a substrate removal and metal deposition.

Consequently there is still a need for an efficient and easilymanufacturable photonics coupling device.

SUMMARY

It is an object of the present disclosure to provide photonics devicesfor coupling radiation that combine good coupling efficiency withsubstantially easy manufacturability.

It is an advantage of embodiments of the present disclosure that, formanufacturing, use can be made of conventionalsemiconductor-on-insulator substrates, without need for complexprocessing steps.

It is an advantage of embodiments of the present disclosure that use canbe made of the silicon photonics platform, allowing a high level ofintegration of components, e.g. active components, in the system.

It is an advantage of embodiments of the present disclosure that use canbe made of systems suffering only little from thermal dependency, whilenot requiring complex manufacturing steps.

The above objective is accomplished by a method and device according tothe present disclosure.

The present disclosure relates to a semiconductor photonics device forcoupling radiation to a semiconductor waveguide, the photonics devicecomprising a semiconductor-on-insulator substrate comprising asemiconductor substrate, a buried oxide layer positioned on top of thesemiconductor substrate, and the semiconductor waveguide on top of theburied oxide layer to which radiation is to be coupled. The photonicsdevice also comprises a grating coupler positioned on top of the buriedoxide layer and configured for coupling incident radiation to thesemiconductor waveguide. The semiconductor substrate has a recessedportion at the backside of the semiconductor substrate for receivingincident radiation to be coupled to the semiconductor waveguide via thebackside of the semiconductor substrate and the grating coupler. It isto be noticed that the optical path can be reversed and therefore thedevice is equally suitable for coupling radiation from the semiconductorwaveguide, via the grating coupler out and the backside of thesemiconductor substrate.

It is an advantage of embodiments of the present disclosure that bycoupling radiation from the backside of the SOI substrate one can makeuse of standard SOI wafers for the manufacturing of the photonicsdevice. It is an advantage of embodiments of the present disclosure thatgood efficiency of the photonics device is obtained.

The photonics device furthermore may comprise a reflector positioned ontop of the grating coupler for reflecting radiation that has notinteracted with the grating coupler during the first pass. By reflectingthe radiation back to the grating coupler, a higher coupling efficiencycan be obtained. It is an advantage of embodiments of the presentdisclosure that avoiding introduction of the mirror between the basicsubstrate and the buried oxide layer, allows to make use of an efficientsystem, without the need for complex manufacturing steps. In prior art,manufacturing typically requires the deposition of multiple layers priorto performing the silicon layer transfer. As the layers need to bedeposited and cannot be grown on the substrate, the bonding process andwafer splitting process are more difficult resulting in lower bondingquality, higher defect counts, and excessive wafer bowing. In theseapproaches, use cannot be made of off-the-shelve substrates and custommade substrates are required. Due to their specific arrangements, usecan be made from off-the-shelve substrates for manufacturing devicesaccording to embodiments of the present disclosure.

It is an advantage of embodiments of the present disclosure thatradiation can be coupled in via a thinned substrate portion, as thisincreases the overall coupling efficiency as more radiation will reachthe grating coupler.

The recessed portion at the backside of the semiconductor substrate mayhave a thickness of less than 50 μm. In order to have close proximityfor coupling of radiation, the recessed portion may be as thin aspossible, without or only with limited hampering of the mechanicalstability of the substrate.

The waveguide coupler may be a SiN waveguide coupler. It is an advantageof embodiments of the present disclosure that these allow the use of SiNcouplers in the devices as SiN is subject to low losses, has a lowthermal dependency, and has a high tolerance to fabrication variation.It is an advantage of embodiments according to the present disclosurethat SiN gratings have a substantially large bandwidth.

The semiconductor-on-insulator substrate may be a silicon-on-insulatorsubstrate and the semiconductor waveguide may be a silicon waveguide. Itis an advantage of embodiments of the present disclosure that thesilicon photonics platform offers a platform for active devices such asmodulators and detectors, thus allowing a high level of integration.

The reflector may be a distributed Bragg reflector. It is an advantageof embodiments of the present disclosure that use can be made of awell-known and efficient reflector.

The distributed Bragg reflector may comprise a stack of alternating SiO₂and Si layers or a stack of alternating SiO₂ and SiN layers. Inembodiments of the present disclosure, as the structure is usedinversely with respect to conventional structures, the reflector, e.g.the distributed Bragg reflector, can be provided on top of thesubstrate, the grating coupler and the waveguide, so that it can beapplied with conventional deposition techniques, without the need forfirst removing other materials.

The reflector may be a reflective metal layer, such as for example analuminum layer.

The present disclosure also relates to an optical system, the opticalsystem comprising at least one photonics device as described above andat least one active device integrated in the photonics device.

The system furthermore may comprise an optical fiber for beingpositioned near or in a recessed portion of the photonics device forcoupling radiation between the optical fiber to the semiconductorwaveguide.

The present disclosure also relates to a method for coupling radiationto a semiconductor waveguide, the method comprising providing incidentradiation, incident via a backside of a semiconductor on insulatorsubstrate, coupling radiation via a grating coupler to a semiconductorwaveguide, the grating coupler and the semiconductor waveguide beingpositioned at a front side of the semiconductor-on-insulator-substrate.The method also may comprise reflecting radiation that was not coupledby the grating coupler at a reflector positioned on top of the gratingcoupler. It is an advantage of embodiments according to the presentdisclosure that efficient radiation coupling can be performed asradiation, not coupled by the grating coupler when the radiation isfirst incident, is reflected again to the coupler, resulting in afurther interaction of the radiation with the grating coupler.

Providing incident radiation may comprise providing incident radiationat a recessed portion via the backside of the semiconductor-on-insulatorsubstrate.

The present disclosure also relates to a method for coupling radiationto an optical fiber from a semiconductor waveguide, the methodcomprising providing an incident radiation wave in a semiconductorwaveguide, coupling radiation coming from the semiconductor waveguidevia a grating coupler through the semiconductor-on-insulator substrate,and receiving the radiation coupled through thesemiconductor-on-insulator substrate in the optical fiber positioned atthe backside of the semiconductor-on-insulator substrate.

Receiving the radiation in the optical fiber may comprise positioningthe optical fiber in a recess at the backside of thesemiconductor-on-insulator substrate.

The present disclosure also relates to a method for manufacturing aphotonics device suitable for coupling radiation to a semiconductorwaveguide, the method comprising obtaining a semiconductor-on-insulatorsubstrate comprising a semiconductor substrate, a buried oxide layerpositioned on top of the semiconductor substrate and a semiconductorwaveguide on top of the buried oxide layer to which radiation is to becoupled, providing a grating coupler in or on an upper layer of thesemiconductor-on-insulator substrate at a front side of thesemiconductor-on-insulator substrate, and providing a recess in thesemiconductor substrate of the semiconductor-on-insulator substrate atthe backside of the semiconductor-on-insulator substrate.

The method furthermore may comprise providing a reflector at a frontside of the semiconductor-on-insulator substrate, the reflectoroverlaying the grating coupler and being suitable for reflectingradiation incident via the backside of the semiconductor substrate andhitting the reflector without being coupled first to the semiconductorwaveguide.

Particular and preferred aspects of the disclosure are set out in theaccompanying independent and dependent claims. Features from thedependent claims may be combined with features of the independent claimsand with features of other dependent claims as appropriate and notmerely as explicitly set out in the claims.

These and other aspects of the disclosure will be apparent from andelucidated with reference to the embodiment(s) described hereinafter.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 illustrates an example photonic device for backside radiationcoupling according to an embodiment of the present disclosure.

FIG. 2 illustrates an example photonic device for backside radiationcoupling comprising furthermore a reflector above the semiconductorwaveguide for reflecting radiation that was not coupled yet, accordingto an embodiment of the present disclosure.

FIG. 3 illustrates an example optical system comprising a photonicsdevice according to an embodiment of the present disclosure.

FIGS. 4a through 4f illustrate examples of the different intermediatestates during the manufacturing of a photonic device in an exemplarymanufacturing method according to an embodiment of the presentdisclosure.

The drawings are only schematic and are non-limiting. In the drawings,the size of some of the elements may be exaggerated and not drawn onscale for illustrative purposes.

In the different drawings, the same reference signs refer to the same oranalogous elements.

DETAILED DESCRIPTION

The present disclosure will be described with respect to particularembodiments and with reference to certain drawings but the invention isnot limited thereto but only by the claims. The drawings described areonly schematic and are non-limiting. In the drawings, the size of someof the elements may be exaggerated and not drawn on scale forillustrative purposes. The dimensions and the relative dimensions do notcorrespond to actual reductions to practice of the invention.

Furthermore, the terms first, second and the like in the description andin the claims, are used for distinguishing between similar elements andnot necessarily for describing a sequence, either temporally, spatially,in ranking or in any other manner. It is to be understood that the termsso used are interchangeable under appropriate circumstances and that theembodiments of the disclosure described herein are capable of operationin other sequences than described or illustrated herein.

Moreover, the terms top, under and the like in the description and theclaims are used for descriptive purposes and not necessarily fordescribing relative positions. It is to be understood that the terms soused are interchangeable under appropriate circumstances and that theembodiments of the disclosure described herein are capable of operationin other orientations than described or illustrated herein.

It is to be noticed that the term “comprising”, used in the claims,should not be interpreted as being restricted to the means listedthereafter; it does not exclude other elements or steps. It is thus tobe interpreted as specifying the presence of the stated features,integers, steps or components as referred to, but does not preclude thepresence or addition of one or more other features, integers, steps orcomponents, or groups thereof. Thus, the scope of the expression “adevice comprising means A and B” should not be limited to devicesconsisting only of components A and B. It means that with respect to thepresent disclosure, the only relevant components of the device are A andB.

Reference throughout this specification to “one embodiment” or “anembodiment” means that a particular feature, structure or characteristicdescribed in connection with the embodiment is included in at least oneembodiment of the present disclosure. Thus, appearances of the phrases“in one embodiment” or “in an embodiment” in various places throughoutthis specification are not necessarily all referring to the sameembodiment, but may. Furthermore, the particular features, structures orcharacteristics may be combined in any suitable manner, as would beapparent to one of ordinary skill in the art from this disclosure, inone or more embodiments.

Similarly it should be appreciated that in the description of exemplaryembodiments of the disclosure, various features of the disclosure aresometimes grouped together in a single embodiment, figure, ordescription thereof for the purpose of streamlining the disclosure andaiding in the understanding of one or more of the various inventiveaspects. This method of disclosure, however, is not to be interpreted asreflecting an intention that the claimed invention requires morefeatures than are expressly recited in each claim. Rather, as thefollowing claims reflect, inventive aspects lie in less than allfeatures of a single foregoing disclosed embodiment. Thus, the claimsfollowing the detailed description are hereby expressly incorporatedinto this detailed description, with each claim standing on its own as aseparate embodiment of this disclosure.

Furthermore, while some embodiments described herein include some butnot other features included in other embodiments, combinations offeatures of different embodiments are meant to be within the scope ofthe disclosure, and form different embodiments, as would be understoodby those in the art. For example, in the following claims, any of theclaimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are setforth. However, it is understood that embodiments of the disclosure maybe practiced without these specific details. In other instances,well-known methods, structures and techniques have not been shown indetail in order not to obscure an understanding of this description.

Where in embodiments of the present disclosure reference is made to aphotonics device, reference is made to a device made using a photonicsplatform based on for example semiconductor-on-insulator substrates suchas silicon-on-insulator substrates, integrated waveguides based on forexample silicon, germanium, silicon germanium, silicon nitride, siliconcarbide, etc. Advantageously a photonics device according to embodimentsof the present disclosure is based on a silicon-on-insulator substratein a silicon photonics platform, which is a very interesting materialsystem for highly integrated photonic circuits. The high refractiveindex contrast allows photonic waveguides and waveguide components withsubmicron dimensions to guide, bend and control light on a very smallscale so that various functions can be integrated on a chip. Suchwaveguides allow a high level of miniaturization, which is advantageous.Furthermore for such waveguide types radiation can be efficientlycoupled in and out the photonics integrated circuit. Usingsilicon-on-insulator also has some technological advantages. Due to theCMOS industry, silicon technology has reached a level of maturity thatoutperforms any other planar chip manufacturing technique by severalorders of magnitude in terms of performance, reproducibility, throughputand cost. Nano-photonic ICs can be fabricated with waferscale-processes, which means that a wafer can contain a large number ofphotonic integrated circuits.

When in embodiments of the present disclosure reference is made to anactive device, reference is made to at least one component such as forexample an integrated detector or an integrated radiation source or anintegrated modulator. Other components also can be easily integrated ina photonics device made in a silicon photonics platform, such as forexample an integrated optical cavity, an integrated optical resonator,an integrated optical coupler, a waveguide, a taper, a tunable filter, aphase-shifter, a modulator or a combination thereof.

Where in embodiments according to the present disclosure reference ismade to the backside of a semiconductor substrate, reference is made tothe opposite side of the semiconductor substrate than the side where thewaveguide is present. In embodiments of the present disclosure thiscorresponds with the side of the substrate where the BOX is deposited.

Where in embodiments according to the present disclosure reference ismade to a grating coupler, reference is made to a coupler for couplingincident radiation from one direction into another direction, e.g. intoan optical element by guiding radiation in another direction. Such agrating coupler may be based on a periodic structure. It may haveperiodicity in one direction, periodicity in two directions, etc.

In a first aspect, embodiments of the present disclosure relate to asemiconductor photonics device for a coupling radiation to or from asemiconductor waveguide. Such coupling may be performed, for example, toor from an optical fiber or to or from free space. The photonics devicemay comprise a semiconductor-on-insulator substrate comprising asemiconductor substrate, a buried oxide layer positioned on top of thesemiconductor substrate, and the semiconductor waveguide on top of theburied oxide layer. Such a semiconductor-on-insulator substrate may befully based on a conventionally available semiconductor-on-insulatorsubstrates. More particularly, it is an advantage of embodiments of thepresent disclosure that for manufacturing the photonics device, aconventional semiconductor-on-insulator substrate may be used, withoutthe need for too much complex processing for altering the existing layerof the substrate. The function of the photonics device may be to coupleradiation from or to the semiconductor waveguide. According toembodiments of the present disclosure, the photonics device mayfurthermore comprise a grating coupler positioned on top of the buriedoxide layer and configured for coupling incident radiation to or fromthe semiconductor waveguide. Furthermore, according to embodiments, thesemiconductor substrate has a recessed portion at the backside of thesemiconductor substrate for receiving incident radiation to be coupledto the semiconductor waveguide via the backside of the semiconductorsubstrate and the grating coupler. In view of reversibility of opticalpath, the device can also be used to couple, via the recess radiationfrom the semiconductor waveguide over the grating coupler via thebackside of the semiconductor substrate radiation to an optical fiber,e.g. positioned in the recess, or to free space.

By way of illustration, embodiments of the present disclosure not beinglimited thereto, advantages and standard and optional features ofparticular embodiments of the present disclosure will be described withreference to FIGS. 1 and 2. FIG. 1 illustrates a photonics device 100according to an embodiment where no additional reflector is present,whereas in FIG. 2, a similar photonics device 200 is shown, but anadditional reflector 210 is introduced for increasing the couplingefficiency.

The photonics devices 100 and 200 of the particular examples are basedon semiconductor-on-insulator substrates 110. Such SOI substrates 110may be any type of SOI substrate. Nevertheless, advantageouslysilicon-on-insulator substrates can be used as they are readilyavailable, have good properties for integrating optical active devices,and provide a well-developed platform. The SOI substrates 110 maycomprise a semiconductor substrate which may be made of any suitablesemiconductor material, e.g. being germanium but in the present examplesbeing silicon substrates, supporting a buried oxide layer 120. Thesemiconductor substrate may comprise a recess introduced from thebackside. Such a recess allows coupling of radiation through thebackside of the semiconductor substrate towards or from opticalcomponents positioned at the other side of the semiconductor substrate.

The thickness of the semiconductor substrate at not-recessed portionsmay be between 650 μm and 800 μm for conventional SOI substrates. Inorder to allow close proximity for the radiation coupling,advantageously the recessed portion 112, where the substrate is thinned,has a thickness below 50 μm, e.g. in the range 0 μm to 50 μm.Advantageously the thickness is selected to provide sufficient strengthbut also close proximity for the radiation coupling. The recessedportion is in area sufficiently large to cover the grating area of thegrating that will be discussed further. More generally, the recessedportion may be large enough to couple all radiation in the radiationspot incident on the substrate towards the semiconductor waveguide. Therecessed portion can be introduced by processing the substrate in anysuitable way such as for example by etching, grinding, milling, laserprocessing such as laser ablation, etc. On top of the semiconductorsubstrate 110, as described above, a buried oxide layer 120 is provided.

The buried oxide layer 120 may have a thickness in the range 1 μm to 4μm. In one example, where the SOI is a silicon-on-insulator substrate,the buried oxide layer is a silicon oxide layer. On top of the buriedoxide layer 120, a semiconductor layer is present, wherein, according toembodiments of the present disclosure, a semiconductor waveguide 130 ispositioned. The semiconductor waveguide 130 in one particular example isa silicon waveguide. It is an advantage of at least some embodimentsaccording to the present disclosure that a silicon waveguide is used, asthis allows introduction of optional active components. Examples of suchactive components are detectors—the photonics device then may besuitable for coupling radiation into the waveguide—, radiation sourcessuch as for example integrated radiation sources like integratedlasers—the photonics device then may be suitable for coupling radiationout of the device—, optical modulators, etc. Such active components alsomay be introduced in other platforms, but the silicon photonics platformadvantageously has been developed already so that good techniques areknown for manufacturing or introduction of these components. Asindicated above, also more passive components can be present in or nearthe semiconductor waveguide. An example position where components may beintroduced is shown in FIG. 2 by arrow 220.

According to embodiments of the present disclosure, the device 100furthermore comprises a grating coupler 140 for coupling incidentradiation from or to the semiconductor waveguide 130. Such a gratingcoupler 140 may have a periodic structure and can have a one-dimensionalperiodicity or a two-dimensional periodicity. According to embodimentsof the present disclosure the grating coupler 140 also may have otherfeatures. The grating coupler 140 may be an apodized grating. Inembodiments of the present disclosure, the grating coupler 140 may bemade using silicon nitride as a guiding layer. The grating coupler maybe a periodic structure in a SiN waveguide. The grating coupler may thencouple to the semiconductor waveguide.

In particular embodiments according to the present disclosure, thephotonics device furthermore comprises a reflector positioned above thegrating coupler. Such a reflector may be any type of reflectorreflecting radiation that was not coupled to the waveguide during thefirst pass at the grating coupler, back into the direction of thegrating coupler. In this way, the chance for coupling is increased andthe efficiency of the photonics device coupler is increased as well. Inparticular embodiments, the reflector may be a distributed Braggreflector (DBR). One example of a DBR is a stack of alternating SiO₂ andSi layers or a stack of alternating SiO₂ and SiN layers. Another exampleof a reflector is a metal layer, e.g. an aluminum layer.

In another aspect, the present disclosure relates to an optical systemfor handling radiation. The optical system comprises a photonics deviceas described in the first aspect and furthermore comprises an opticalfiber, positioned in the recess of the photonics device and adapted forproviding a radiation beam to be coupled to the semiconductor waveguidein the photonics device via the backside of the semiconductor substrate.The optical fiber may be coupled to the recessed portion of thesubstrate. Such a coupling may be made using any suitable means such asfor example using an optical glue. The optical fiber may be coupled atone side with the photonics device and at the other side directly orindirectly with a radiation source or a detector for detectingradiation. The optical system furthermore may comprise additionaloptical components. As described above, also a number of components,active or passive, may be present in the photonics device. Opticalsystems that benefit from embodiments according to the presentdisclosure may be any type of optical system, such as for example anoptical detection system, an optical communication system, an opticaldata processing system, etc. By way of illustration, embodiments of thepresent disclosure not being limited thereto, an example of an opticalsystem 300 is shown in FIG. 3, indicating a first optical subsystem 310,an optical fiber 150 optically linking the first optical subsystem 310with a photonics device 100 which links with a second optical subsystem320.

In yet a further aspect, the present disclosure relates to a method forcoupling radiation to a semiconductor waveguide. According toembodiments, the method comprises providing incident radiation, incidentvia a backside of a semiconductor on insulator substrate, coupling theradiation via a grating coupler to a semiconductor waveguide, thegrating coupler being positioned at a front side of the semiconductor oninsulator substrate. In some embodiments, the provision of radiationincident via a backside of the semiconductor-on-insulator may beprovision of radiation in a recessed portion of the substrate at thebackside of the substrate in the semiconductor on insulator substrate.In some particular embodiments, the method also comprises reflectingradiation that was not coupled by the grating coupler back to thegrating coupler. For such reflecting, a reflector positioned on top ofthe grating coupler may be used. The method furthermore may comprisesteps expressing the functionality of components of the photonics deviceor of the optical system.

In still a further aspect, the present disclosure relates to a methodfor coupling radiation to an optical fiber from a semiconductorwaveguide. The method comprises providing an incident radiation wave ina semiconductor waveguide, coupling radiation coming from thesemiconductor waveguide via a grating coupler through thesemiconductor-on-insulator substrate, and receiving the radiationcoupled through the semiconductor-on-insulator substrate in the opticalfiber positioned at the backside of the semiconductor-on-insulatorsubstrate. In particular embodiments, the optical fiber may bepositioned in a recess at the backside of the semiconductor-on-insulatorsubstrate. In other embodiments, the method may comprise redirectingradiation that has been directed by the grating coupler to the frontside of the semiconductor-on-insulator substrate by reflecting it backin the direction of the backside of the semiconductor-on-insulatorsubstrate. The method furthermore may comprise steps expressing thefunctionality of components of the photonics device or of the opticalsystem.

In one aspect, the present disclosure relates to a method formanufacturing a photonics device suitable for coupling radiation to asemiconductor waveguide. The method comprises obtaining asemiconductor-on-insulator substrate comprising a semiconductorsubstrate, a buried oxide layer positioned on top of the semiconductorsubstrate, and a semiconductor waveguide on top of the buried oxidelayer to which radiation is to be coupled. It is an advantage ofembodiments of the present disclosure that conventionalsemiconductor-on-insulator substrates can be used. Alternatively, asemiconductor-on-insulator substrate also may be manufactured using forexample conventional semiconductor processing techniques.

The method also comprises providing a grating coupler in or on an upperlayer of the semiconductor-on-insulator substrate at a front side of thesemiconductor-on-insulator substrate. Producing a grating coupler, e.g.a SiN grating coupler on a silicon-on-insulator substrate, can beperformed using conventional semiconductor processing techniques. Themethod also comprises providing a recess in the semiconductor substrateof the semiconductor-on-insulator substrate at the backside of thesemiconductor-on-insulator substrate. Such a recess may be obtainedusing any suitable technique, such as for example laser ablation,milling, grinding, etching, etc. The method furthermore may compriseproviding a reflector at a front side of the semiconductor-on-insulatorsubstrate, the reflector overlaying the grating coupler and beingsuitable for reflecting radiation incident via the backside of thesemiconductor substrate and hitting the reflector without being coupledfirst to the semiconductor waveguide. Providing a reflector may beperformed using conventional semiconductor processing techniques.

FIGS. 4a to 4f illustrate example intermediate states of the deviceduring the manufacturing of the photonics device according to anexemplary method according to an embodiment of the present disclosure,illustrating standard and optional features of a manufacturing process.

In a first step, a semiconductor-on-insulator substrate is obtained. Itthereby is an advantage of embodiments of the present disclosure thatthe substrate may be an off-the-shelve substrate. Nevertheless,alternatively the semiconductor-on-insulator substrate also may beobtained by manufacturing using a number of processing steps, known bythe person skilled in the art. The semiconductor-on-insulator substrateis shown in FIG. 4a . The semiconductor substrate 110, in the presentexample being a Si substrate, the buried oxide layer 120, in the presentexample being a SiO2 layer, and the semiconductor layer 401 wherein thesemiconductor waveguide 130 will be formed, in the present example beinga Si layer, are shown.

In a second step, the waveguide 130 as well as possible activecomponents are formed. Methods for forming such a waveguide are as suchwell known to the person skilled in the art and will not be furtherdescribed in detail. The resulting waveguide 130 is shown in FIG. 4b .Additional layers introduced during the processing are also shown. Thisincludes in the present example a Ge component 403 as well as additionallayers 402 which may be used as cladding layers for the waveguide arealso shown.

In a following step, the grating coupler 140, in the present examplebeing a SiN grating coupler, is introduced. The grating coupler 140 isshown in FIG. 4 c.

In a further optional step, electrical contacts 404 are provided forcontacting the active components, e.g. radiation source or detector.These are shown in FIG. 4 d.

In yet a further optional step, the reflector 210 is introduced. In thepresent case, the reflector is a DBR reflector positioned above the SiNgrating coupler 140, as can be seen in FIG. 4 e.

In a final step, the recess is produced in the backside of the substrate110, resulting in a recessed portion 112. The latter is seen in FIG. 4f.

The above illustrates an exemplary flow for manufacturing a photonicsdevice, but it will be understood by the person skilled in the art thatother processing steps and particular processing techniques can be usedwhere appropriate, embodiments not being limited thereby.

What is claimed is:
 1. A semiconductor photonics device for couplingradiation to a semiconductor waveguide, the semiconductor photonicsdevice comprising: a semiconductor-on-insulator substrate comprising: asemiconductor substrate, a buried oxide layer positioned on top of thesemiconductor substrate, and a semiconductor layer positioned on top ofthe buried oxide layer, wherein the semiconductor layer comprises asemiconductor waveguide to which radiation is to be coupled; and a SiNgrating coupler positioned above the buried oxide layer and comprising aSiN guiding layer, wherein the SiN guiding layer is positioned above thesemiconductor layer, and wherein the SiN grating coupler is configuredfor coupling incident radiation to the semiconductor waveguide, whereinthe semiconductor substrate has a recessed portion at the backside ofthe semiconductor substrate for receiving incident radiation to becoupled to the semiconductor waveguide via the backside of thesemiconductor substrate and the SiN grating coupler.
 2. Thesemiconductor photonics device according to claim 1, further comprisinga reflector positioned on top of the SiN grating coupler for reflectingradiation that has not interacted with the SiN grating coupler during afirst pass.
 3. The semiconductor photonics device according to claim 2,wherein the reflector is a distributed Bragg reflector or a metalreflector.
 4. The semiconductor photonics device according to claim 3,wherein the reflector is a distributed Bragg reflector comprising astack of alternating SiO₂ and Si layers or a stack of alternating SiO₂and SiN layers.
 5. The semiconductor photonics device according to claim1, wherein the recessed portion at the backside of the semiconductorsubstrate has a thickness of less than 50 μm.
 6. The semiconductorphotonics device according to claim 1, wherein thesemiconductor-on-insulator substrate is a silicon-on-insulatorsubstrate, and wherein the semiconductor waveguide is a siliconwaveguide.
 7. The semiconductor photonics device according to claim 6,wherein the SiN guiding layer is separated from the silicon waveguide bya cladding layer.
 8. An optical system, the optical system comprising: asemiconductor photonics device comprising: a semiconductor-on-insulatorsubstrate comprising a semiconductor substrate, a buried oxide layerpositioned on top of the semiconductor substrate, and a semiconductorlayer positioned on top of the buried oxide layer, wherein thesemiconductor layer comprises a semiconductor waveguide to whichradiation is to be coupled, and a SiN grating coupler positioned abovethe buried oxide layer and comprising a SiN guiding layer, wherein theSiN guiding layer is positioned above the semiconductor layer, andwherein the SiN grating coupler is configured for coupling incidentradiation to the semiconductor waveguide, wherein the semiconductorsubstrate has a recessed portion at the backside of the semiconductorsubstrate for receiving incident radiation to be coupled to thesemiconductor waveguide via the backside of the semiconductor substrateand the SiN grating coupler; and an active device integrated in thesemiconductor photonics device.
 9. The optical system according to claim8, further comprising an optical fiber positioned near or in therecessed portion of the semiconductor photonics device for couplingradiation between the optical fiber to the semiconductor waveguide. 10.The optical system according to claim 8, wherein the semiconductorphotonics device further comprises a reflector positioned on top of theSiN grating coupler for reflecting radiation that has not interactedwith the SiN grating coupler during a first pass.
 11. The optical systemaccording to claim 10, wherein the reflector is a distributed Braggreflector or a metal reflector.
 12. The optical system according toclaim 8, wherein the recessed portion at the backside of thesemiconductor substrate has a thickness of less than 50 μm.
 13. A methodfor manufacturing a semiconductor photonics device suitable for couplingradiation to a semiconductor waveguide, the method comprising: obtaininga semiconductor-on-insulator substrate comprising a semiconductorsubstrate, a buried oxide layer positioned on top of the semiconductorsubstrate, and a semiconductor layer positioned on top of the buriedoxide layer; forming a semiconductor waveguide on top of the buriedoxide layer; providing a SiN grating coupler comprising a SiN guidinglayer, wherein the SiN guiding layer is provided above the semiconductorlayer; and providing a recess in the semiconductor substrate of thesemiconductor-on-insulator substrate at the backside of thesemiconductor-on-insulator substrate.
 14. The method according to claim13, further comprising providing a reflector at the front side of thesemiconductor-on-insulator substrate, the reflector overlaying the SiNgrating coupler and being suitable for reflecting radiation incident viathe backside of the semiconductor substrate and hitting the reflectorwithout being coupled first to the semiconductor waveguide.
 15. Themethod according to claim 14, wherein the reflector comprises adistributed Bragg reflector or a metal reflector.
 16. The methodaccording to claim 13, wherein the recess has a thickness of less than50 μm.